1. Field of the Invention
The present invention relates to a method of sharing various types of medium drives and a recording/ reproduction apparatus including a medium controller for practicing the method.
2. Description of the Related Art
In a magnetic recording/reproduction apparatus including a floppy disk drive (FDD), the same recording medium must be able to be used in different floppy disk drives, and accurate data-access must be achieved.
A plurality of concentric tracks for recording data are formed on a recording medium. FIG. 1 illustrates the format of each track. Each sector has an identification (ID) field and a data field. For example, in an MFM recording, the ID field is separated from the data field by GAP2 field in which 22 bytes of data (4E).sub.H are written. The ID field includes a SYNC subfield in which data (00).sub.H is written and an ID subfield in which an identification code is written. The data field includes a SYNC subfield in which data (00).sub.H is written and a data subfield in which recording data is written. The adjacent sectors are separated from each other by GAP3 field. Assume that data are recorded on each track of the medium, fully across the track. If the recording medium is set slightly eccentrically to the drive, or the recording medium is warping, the head of the drive would be a little off the track. In this case, a portion of the head is located above the adjacent track, and the head will inevitably read the recorded data from not only the target track but also the adjacent track.
In order to avoid the disk drive reading the recorded data from the tracks adjacent to the target track, a gap is provided between tracks to make the track width narrower than the track pitch. To provide the gap, the conventional floppy disk drive is provided with a tunnel erase head or a straddle head. The head records data on each track, and, at the same time, erases the recorded data from either side of the target track by a predetermined width.
The typical straddle head comprises a read/write (R/W) core having a R/W gap and erase cores each located on either side of the R/W gap, having an erase gap being provided between the R/W core and erase core. At the same time a data signal is supplied to a R/W coil wound around the R/W core for data writing, an erase signal is supplied to an erase coil wound around each erase core thereby erasing the data signals recorded on both side portions of the target track by a predetermined width. However, since the R/W gap and erase gap are located very close to each other, the output of the straddle head has a low S/N ratio. Because of the low S/N ratio, the straddle head is not usually used in a floppy disk drive. Rather, the tunnel erase head type drive is typically used in the conventional floppy disk drive.
As shown in FIG. 2, a tunnel erase head comprises R/W head 106 having a R/W core having a R/W gap 116 and a coil wound around the core, and an erase head 108 disposed behind R/W head 106. Erase head 108 has two erase gaps 118 aligned with the ends of R/W gap 116. A data signal is supplied to the R/W coil wound around the R/W core, while an erase signal is supplied to the erase coil wound around the erase core. Therefore, following the recording of data signals on the recording medium, the data signals recorded on both side portions of the target track are erased.
According to the tunnel erase head type FDD, erase gaps 118 are located behind R/W gap 116 by distance X.sub.T. Hence, in order to accurately erase the data signals recorded on both sides of the target track from the position where the signal recording on the track has started to the position where the signal recording is ended, the supply of the erase signal to the erase coil must be delayed by time .DELTA. T.sub.TON from the start of the data recording. Stopping the supply of the erase signal must be delayed by time .DELTA. T.sub.TOFF from the end of the recording thereof.
The following relationship is given EQU .DELTA. T.sub.TON =.DELTA. T.sub.TOFF =X.sub.t /V.sub.T =.DELTA. T.sub.T
where V.sub.T is the linear velocity at which the recording medium moves relative to the tunnel erase head.
In recording data on a recording medium, a host computer supplies the floppy disk controller (FDC) with a timing signal representing the record-starting time and the record-ending time. The timing signal is supplied to a control circuit provided within the FDC. The control circuit outputs write gate signal WG and erase gate signal EG to the FDD. In the FDD, signal WG will be used to supply a write data signal WD to the R/W coil. Signal EG is delayed by time .DELTA. T.sub.T from the signal WG. In this case, the recording medium is rotated at a constant speed, and hence, linear velocity V.sub.T of the recording medium relating to the magnetic head varies depending on the tracks. Therefore, it is desired that time .DELTA. T.sub.T be changed whenever the head moves from one track to another.
Generally, however, time .DELTA. T.sub.TON is determined such that the tunnel erase head can entirely erase the data recorded on the track on both sides from a start position where recording of the data is started even when the head is positioned at the outermost track where linear velocity V.sub.T is the maximum. The time .DELTA. T.sub.TOFF is determined such that the tunnel erase head can assuredly erase the data recorded on the track on both sides to a end position where recording of the data is ended even when the head is positioned at the innermost track of the recording medium where the linear velocity V.sub.T is the minimum. More specifically, these times are set as follows: EQU .DELTA. T.sub.TON .ltoreq.X.sub.T /Vin EQU .DELTA. T.sub.TOFF .ltoreq.X.sub.T /Vout
where Vout is the relative linear velocity of the head positioned at the outermost track and Vin is the relative linear velocity of the head positioned at the innermost track. In this case, the closer to the innermost track the head position is, the more over-erased areas exist on both sides at the beginning portion. On the other hand, the closer to the outermost track the head position is, the more over-erased areas exist on both sides at the end portion. Each track is divided into sectors each including so-called "gap regions" preceding and following the data filed as shown in FIG. 1. Gap regions are provided for protecting the data against a fluctuation of the data field, which may happen due to a dimensional error of the floppy disk drive or change in rotational speed of the recording medium. Hexadecimal data FF in FM recording or data 4E in MFM recording is written in these gap field. Since the over-erased areas produced preceding and following the data field fall within these gap fields, there will be no problems.
It is demanded that a floppy disk drive should record data on a recording medium in a high density. As is disclosed in, for example, Toshiba Review, No. 154, Winter 1985, 18-22 pp, a perpendicular recording floppy disk has been developed, which comprises a barium ferrite layer, as a magnetic material, coated on a base film, and has a 4MB recording capacity. The more data that is recorded on a track, or the higher the recording density is, the shorter wavelength the data signals must have. To accurately read signals of short wavelengths, the width of the read gap must be narrower. In most floppy disk drives, the read gap is used also as the write gap so that the write gap inevitably becomes narrower. The narrower the write gap, the smaller the magnetization region defined by the magnetic flux generated in the gap. The depth of the magnetization region being magnetized is said to be about the same as the length of the write gap. Therefore, in order to erase signals completely from a track by overwriting new data on the same track, it is required that the thickness of the magnetic layer be about a quarter of the wavelength of a data signal. This is explained in "The Reproduction Of Magnetically Recorded Signals" written by Wallace, Jr, Bell System Technology Journal, Vol. 30, No. 4, 1951. For instance, with a recording density of 35 KBPI, the read/write gap length must be set at about 0.5 um in consideration of gap loss, and thus the magnetic layer must have a thickness of about 0.5 um or less.
It is difficult, however, to uniformly coat the magnetic material on the base film of the recording medium. Consequently, signal recording is effected only on the surface portion of the magnetic layer, and even after new data have been overwritten on the previously recorded data, the previously written data are left unerased. This undesired phenomenon also takes place when the magnetic layer is made of a magnetic material having a high coercive force.
In order to prevent this phenomenon, a preerase head has been developed. As is illustrated in FIG. 2, the preerase head comprises a R/W Read 104 having a R/W gap 114 and a preerase head 102 provided upstream of the R/W head 104 with respect to the direction of movement of a recording medium. Preerase head 102 has an erase gap 112, which faces read/write gap 114 and is longer and wider than R/W gap 114. According to the preerase type FDD, data signals are recorded on the target track in the following manner. First, an erase signal is supplied to an erase coil wound around an erase core, and the track area is widely erased to the deep area of the magnetic layer of the recording medium by erase gap 112 reaching the recording position on the recording medium, preceding R/W gap 114. As a result, new data are recorded in the data field, from which the previously-recorded data have been completely erased, by R/W gap 114 which reaches this data field following the erase gap 112. Even with a disk having a high recording density in use, therefore, the overwrite characteristic is not deteriorated.
An example of a magnetic recording/reproduction apparatus utilizing the wide preerase type FDD is disclosed in commonly assigned U.S. Pat. Application Ser. No. 067,972 filed on Jun. 30, 1987. In this example, a write gate signal (WG), an erase gate signal (EG) and a write data signal (WD) are sent to the preerase head type FDD from a FDC. According to the aforementioned tunnel erase type FDD, by comparison, only the write gate signal and write data signal are sent to the FDD from the FDC; an erase signal corresponding to the erase gate signal is produced in this FDD in accordance with the received write gate signal.
The phase relationship between the write gate signal and the erase gate signal in the preerase type FDD is opposite to the phase relationship involved in the tunnel erase type FDD. Naturally, the erase gate signal cannot be produced from the write gate signal in the preerase type FDD.
If data recording in the wide preerase type FDD is done using the same write gate signal as used in the tunnel erase type, the following problem would occur. There would be an unerased area produced in the SYNC subfield of the data field, which continues for time .DELTA. Tp(=Xp/Vp), where Vp is the relative speed of the head with respect to the disk and Xp is the distance between R/W gap 114 and erase gap 112. In addition, the gap field GAP3 in FIG. 1 will have an unerased area. Particularly, since the content of the SYNC subfield is used as a sync signal in data reproduction, if the SYNC subfield has a deteriorated overwrite characteristic due to having the unerased area, the S/N ratio of a reproduction signal from the unerased area during reproduction as well as the tracking characteristic of a PLL circuit on the basis of the reproduction signal from the magnetic head are deteriorated.
Because of the above problems, a FDC for the tunnel erase type FDD could not be used for the preerase type FDD. In this respect, therefore, it was necessary to provide two separate FDCs to commonly use the tunnel erase type FDD and the preerase type FDD.